【作者】 李云振；

【导师】 王从曾；

【作者基本信息】 北京工业大学 ， 材料学， 2007， 硕士

【摘要】 粉末冶金材料和制品的烧结是当前新材料制备及加工的重要手段,是决定粉末冶金制品质量的关键技术环节之一。由于新材料制备及加工对烧结方法及工艺的要求日益严酷,相应的新技术也就不断出现,例如热等静压烧结、激光烧结、SPS烧结等,但是这些方法都有自身的使用范围,仍难以满足新材料不断发展的需求,研究开发新的烧结方法仍然是粉末冶金领域的重要课题。本课题所探讨的空心阴极等离子快速高温烧结工艺就是利用空心阴极放电效应作为新的烧结手段,实现对金属的高温快速烧结,在烧结的同时引入渗金属工艺,这样材料表面形成合金化层,可以改善材料的表面性能。铁基粉末的空心阴极烧结过程大致可分为以下三个阶段:黏结阶段﹑烧结颈长大阶段﹑闭孔隙阶段。烧结过程中,孔隙逐渐收缩,最后接近于球形,晶粒会出现再结晶和晶粒长大。烧结过程中试样的致密度随着烧结温度的增加而增加,烧结过程中烧结体致密化明显。铁基粉末空心阴极烧结具有无须其他加热元件提供热能的特点。在铁基粉末空心阴极烧结的同时进行渗镍处理后,可以得到扩散层。这样工件渗镍后具有高的耐蚀性,抗高温氧化性。研究其渗层厚度和致密度的影响因素,得到的结果如下:随着烧结温度的升高,渗层厚度迅速增加;渗层厚度随保温时间的延长而增加。渗镍层组织为一层扩散层,渗层中Ni的浓度分布特点是从渗层表面到基体逐渐降低,而且渗层中Ni原子的浓度比较低。关于扩散渗层的形成,其过程主要由Ni原子在试样表面沉积外延生长及向内扩散所控制,表面沉积的Ni原子数量比扩散进入基体的多,Ni原子在表面的沉积形成Fe-Ni合金相。在铁基粉末空心阴极烧结的同时进行渗钨处理后,可以得到致密的基体组织和钨渗层,这样可以增强表面的耐磨性、红硬性。结果表明:钨渗层的厚度随着烧结温度的升高和保温时间的延长而增加;通过对钨渗层分析可以得出,在不同的工艺条件下,所获得的组织形态大致相同,主要发生γ相向α相的转变,钨渗层为与试样表面垂直的柱状晶α相组织,并且钨渗层与基体之间有明显的界面分开;渗层以及表层的基体中钨元素的含量比较低,并且钨元素的浓度由渗层表面到基体逐渐降低,试样表面形成Fe-W合金相Fe₇W₆。更多还原

【Abstract】 The sintering of powder metallurgy material and product is an important way of preparation and processing of new material currently. The sintering is a key segment of deciding the quality of powder metallurgy product. Because preparation and processing of new material requires sintering method strictly, corresponding new technology appears continously, such as Hot Isostatic Sintering, Laser Sintering, Spark Plasma Sintering, but these methods have their applying area and cannot meet the demand of developing of new material. Researching and designing new sintering method is still an important topic of powder metallurgy field. Hollow Cathode Sintering process use Hollow Cathode Discharging effect as new sintering facility, implement high-speed sintering of metal. Introducing metallic cementation at the same time, thus the surface of material will form alloying layer, it will improve the surface property of material.Hollow Cathode Sintering of iron powder can be divided into three steps: bonding step, sintering neck-growth step, pore-reducing step. In the sintering process, the pore shrinks gradually, it approaches to sphere finally, the grain will appear recrystalization and grain-growth. In the process of sintering, the density of sample will increase as the sintering temperature increases, the body of sintering compacts obviously. Hollow Cathode Sintering of iron powder have advantages as follows: providing heat energy without other heating components.After nickelizing it will obtain nickel layer consist of diffusion layer. Thus the work will have high erosion resistance and anti-high temperature oxidation. We will study the influencing factor of layer thickness and density, The results show that, as the sintering temperature increases, the whole layer thickness increases rapidly, The layer thickness will increase as the keeping time extends. The tissue of nickel layer is diffusion layer, The distributing characteristic of Ni concentration is decreased gradually from the layer surface to the body, but also the concentration of Ni atom is slow. As the formation of diffusion layer, the process is controlled by the extension growth and inward diffusion of Ni content. The content of Ni atoms from surface deposition is larger than those from entering body, Ni atom forms alloy in the surface deposition.At the same time, after tungstenizing it will obtain compact matrix tissue and tungsten layer, thus it will intensify wear property and red-hardness of the surface. The results show that the thickness of tungsten layer will increase as the sintering temperature heightens and the keeping time extends; By the analysis of tungsten layer microstructure, we can ontain: In different conditions, the microstructure is the same, it occurs the transformation fromγphace toαphase, the tissue of layer is columner alloyα, and there have obvious interface between tungsten layer and body, the content of tungsten in the layer or in the body of surface is low, and the concentration of tungsten falls from the surface to body, The surface of sample forms alloy Fe7W6.更多还原